In photolithography techniques, steps are performed in which, for example, a resist film comprising a resist composition is formed on a substrate, then selective exposure is performed on the resist film through a photomask with a predetermined pattern by radiation such as light and electron beams, and developing is performed so as to form a resist pattern having a predetermined shape on the resist film. Resist compositions, in which the exposed portions are converted to be soluble in a developing solution, are referred to as the positive type, and resist compositions, in which the exposed portions are converted to be insoluble in a developing solution, are referred to as the negative type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening of the wavelength of the exposure light. Conventionally, ultraviolet radiation such as g-lines and i-lines have been used as the exposure light, but currently, KrF excimer lasers (248 nm) are being introduced, and ArF excimer lasers (193 nm) are now starting to be introduced. Moreover, F2 excimer lasers (157 nm), EUV (extreme ultraviolet), electron beams, and X rays, whose wavelengths are shorter than those of the above lasers, are also being examined.
Moreover, reproduction of patterns with very fine dimensions requires resist materials with high resolution. As such resist materials, chemically amplified resist compositions comprising a base resin and an acid generator that generates acid by exposure, are used. For example, a chemically amplified positive resist comprises a resin component in which the alkali solubility increases by the action of an acid and an acid generator component that generates acid by exposure, and when an acid is generated from the acid generator by exposure in the formation of a resist pattern, the exposed portions are converted to an alkali soluble state.
Typically, resins such as polyhydroxystyrene (PHS) based resins in which the hydroxyl groups are protected by an acid-dissociable dissolution inhibiting group are used as resin components of chemically amplified positive resist compositions. Moreover, examples of used acid-dissociable dissolution inhibiting groups include: so-called acetal based acid-dissociable dissolution inhibiting groups such as chain-like ether groups typified by a 1-ethoxyethyl group, and cyclic ether groups typified by a tetrahydropyranyl group; and so-called annealing type acid-dissociable dissolution inhibiting groups such as tertiary alkyl groups typified by a tert-butyl group, and tertiary alkoxycarbonyl groups typified by a tert-butoxycarbonyl group (for example, see patent reference 1).
On the other hand, in the production of semiconductor elements and liquid crystal display elements, an impurity diffusion layer is formed on the surface of a substrate. The formation of the impurity diffusion layer is typically performed in two steps of introduction and diffusion of impurities. One of the introduction method is the ion implantation (hereafter referred to as implantation) in which an impurity such as phosphorus and boron is ionized in a vacuum and is accelerated in a high electric field to be injected into the surface of a substrate.
As the method of selectively injecting impurity ions into the surface of a substrate by implantation, for example, the “inclined implantation” process is reported in patent reference 2, in which an inclined substrate with a resist pattern (mask) is subjected to ion implantation. This process is believed to be effective for selective ion injection into small portions of the substrate directly below the resist pattern or into the side walls of holes formed in the substrate.
When a fine resist pattern of about 0.35 μm is formed by the inclined implantation process, a resist pattern serving as a mask must be very thin of about 0.1 to 0.5 μm so as not to inhibit ion implantation.
Furthermore, resist patterns in the inclined implantation process are required to have shape characteristics for injecting ions into desired position in the substrate.
However, in the inclined implantation process using such a thin film resist pattern (hereafter referred to as the thin-film implantation process), particularly, if a highly transparent resin for exposure light is used, the shape of the resist pattern is prone to be defective due to the effect of incident light during the exposure and reflected light from the substrate. In particular, in the production of semiconductor elements and liquid crystal display elements, since the thin-film implantation process is performed on substrates formed with electrodes and the like, it is difficult to form a resist film in an even thickness on these substrates. This results in a problem of a so-called standing wave (hereafter abbreviated as SW), that is a phenomenon in which the dimension of a resist pattern is increased/decreased due to variation in the resist film thickness. The dimensional change of pattern caused by the SW is prone to be increased as the resist film becomes thinner, and as the resist film becomes more transparent. In particular, this problem appears remarkable if the film is as thin as 500 nm or less. Moreover, the problem of the dimensional change becomes more serious as the resist pattern becomes finer.
In response to such a problem, an attempt is being made to suppress the dimensional change by blending a compound (dye) having absorbance of exposure light into a resist (for example, see patent reference 3).
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-341538
[Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. Hei 8-22965
[Patent Reference 3]
Japanese Unexamined Patent Application, First Publication No. 2003-149816